Improved process for the recovery of oil

ABSTRACT

Improved oil recoveries, where the reservoir is flooded with a REM (recovery enhancing material) followed by a mobility control polymer, are obtained by either preceding the injection of the REM with a PCA (polymer conserving agent) or incorporating the PCA in a portion of the REM. The PCA, then, preferentially adsorbs onto available adsorption sites within the subterranean reservoir which otherwise would be occupied by the mobility control polymer. Examples of the PCA include polymers and copolymers of, for instance, acrylamide and sodium acrylate. They generally have an average molecular weight within the range of about 2000 to about 500,000.

l 6 '51 7 3 b H P11 7912; XR 367123399 1? O United States Patent\ 1 911111 3,783,944 Jennings et al. Jan. 8, 1974 {54] MP D P S F RTHE3,482,632 12/1969 HOlm 166/273 VERY OF OIL 3,497,006 2/1970 Jones et a1.166/273 RECO 13,500,921 3/1970 Abrams et al. 166/273 Inventors: RobertJennings, Walnut Creek, 3,523,581 8/1970 Murphy 166/273 Calif.; WilliamM. Thornton, 3,532,166 10/1970 Williams 166/274 Houston, Tex. 3,679,0007/1972 Kaufman 166/273 73 A D w Chem al Com n Midland, 1 sslgnees Mich;Malfzthon gi g Primary Examiner-Stephen J. Novosad n ay 1 1 pa' g g j'Attorney-William M. Yates et al. each (221 F1168? 6613:1972 M'FQM [57]ABSTRACT 1 Improved oil recoveries, where the reservoir is flooded [211Appl' 295204 with a REM (recovery enhancing material) followed by amobility control polymer, are obtained by either [52] US. Cl. 166/274,166/273 preceding the injection of the REM with a PCA (poly- [51] Int.Cl E211) 43/22 [mer conserving agent) or incorporating the PCA in a [58]Field of Search .1 166/274, 273, 275; portion of the REM. The PCA, then,preferentially ad- 252/8-55 D sorbs onto available adsorption siteswithin the subteriranean reservoir which otherwise would be occupied[56] References Cited by the mobility control polymer. Examples of thePCA UNITED TE PA ENT include polymers and copolymers of, for instance,ac- 3 039 529 6/1962 McKennon v 166/275 rylamide and sodium acrylate.They generally have an 312541714 6/1966 Gogarty 6161:1111: 1.1: 166/274average molecular Weight Within the range of about 3,282,337 11/1966 Pye166/275 2 to about 3,476,186 11/1969 Sarem 166/274 15 Claims, N0Drawings 1 IMPROVED PROCESS FOR THE RECOVERY I OF OIL BACKGROUND OF THEINVENTION 1. Field of the Invention Fluids are injected into asubterranean reservoir through an injection means and displaced toward aproduction well to recover crude oil therethrough. Injected fluidsinclude a polymer conserving agent which adsorbs onto the reservoirrock.

2. Prior Art to the Invention It is known that during the flooding of asubterranean reservoir with mobility control polymers, e.g., partiallyhydrolyzed, high molecular weight polyacrylamides and copolymers ofacrylamide and sodium acrylate, the polymer tends to adsorb onto thereservoir rock. This adverse phenomenon degrades the mobility controlproperties imparted by the polymer; i.e., it leaves a low viscosity bankof water which can readily finger through the REM bank. Jones in U.S.P.3,482,631 prevents this adversity by saturating the adsorption siteswith a mobility control agent, e.g., partially hydrolyzed, highmolecular polyacrylamides Jones theory being to occupy adsorption sitesso that a subsequently injected slug will not be adversely affected byactive adsorption sites.

Williams in U.S.Pat. No. 3,532,166 overcomes the adsorption ofpolysaccharides out of aqueous solutions by incorporating within thesolution sacrificial agents such as water soluble carbonates and/orwater soluble, inorganic polyphosphates.

Murphy in U.S. Pat. No. 3,523,581 prevents adsorption of viscosifiers byadmixing with an aqueous solution containing the viscosifier asacrificial agent which preferentially adsorbs on the surfaces of thereservoir rock; examples of the agents include alkali metalpolyphosphates.

To improve oil recoveries of secondary and tertiary recovery processes,the art teaches that surfactant systems such as water-external andoil-external emulsions and micellar dispersions are useful. Examples ofsuch systems are taught in the following U.S. Pat. Nos: 3,275,075 toGogarty et al.; 3,506,070 and 3,506,071 to Jones; 3,497,006 to Jones etal.; 3,330,344 and 3,348,611 to Reisberg; 3,126,952 to Jones; 3,373,809to Cooke, Jr.; 3,288,213 to King et al.; 3,163,214 to Csaszar; and3,302,713 to Ahearn et a1. However, the surfactant systems must includemobility control to obtain maximum oil recovery. Most of the mobilitycontrol polymers tend to be leached out of solution when passing throughreservoir rock due to adsorption of the polymer on the reservoirrock.The effect, of course, is degradation of mobility control, adverselyinfluencing oil recovery results.

SUMMARY OF THE INVENTION It has now been found that the problemsinherent in the use of an aqueous polymeric material to drive a residualoil recovery enhancing material through a formation whose natural driveenergy has been depleted can be essentially eliminated by the use of apolymer conserving agent ahead of said enhancing material.

More particularly the invention comprises a sequential method forintroducing into a formation which contains residual oil, said formationhaving been depleted of its natural drive energy, first, a polymerconserving agent, secondly a recovery enhancing material, and lastly, anaqueous solution of a polymeric flooding material for mobility control.

2 DETAILED DESCRIPTION OF THE INVENTION The displacing or flooding mediawhich are suitable herein comprise water containing from 0.001 to 0.5weight percent, preferably 0.01 to 0.15%, of a watersoluble organicmobility control polymer having a molecular weight of at least about 1.5X 10 preferably at least about 2,5 X 10 Said polymers are of the formulaW ene-f;

ll izfll I T/Ql iii: l.

wherein R and R are, independently, H or CH;,; Y is H ;NI-I or an alkali(such as Na or K") or alkaline earth (such as Mg or Ca) metal ion; m is0 to 100, preferably 0 to about 33; m n +p equal Z wherein R is H or CHand X is wherein X, is o-Y+, 1 1H2 or 011 B, being CH3 or CH CH or R'awherein R and R are, independently, H or -CH;;.

a Phi instance, polymers containing one or more of the monomersacrylamide, acrylic acid (and ammonium, alkali and alkaline earth metalsalts thereof), acrylonitrile, vinyl acetate, vinyl formate, methylvinyl ether.

crylamide, N-acryltaurine, N-(2-hydroxyethyl)- acrylamide,N-(diacetonyl)-acrylamide, and the like Pye, Sarem (Col. 3, line 64 toCo]. 8, line 67), and Hedrick; salts of itaconic acid Von Engelhardt andHedrick; maleic and maleamic acids, salts and half-esters thereof VonEngelhardt and Hedrick; and styrene,

vinyl toluene and alpha-methylstyrene sulfonates Pye (Col. 5, line 28 toC01. 6, line 5) and Hedrick.

Von Engelhardt (Col. 1, lines 59-66 and Col. 2, lines 16-28) furthershows the preparation of salts of some of the above.

Homopolymers and copolymers of acrylamide and acrylic acid or its saltsdemonstrate no solubility problems. However, it must be borne in mindthat certain monomers characterized as A in the formula above must besolubilized. For instance, incorporation of more than about 65 weightpercent acrylonitrile retards solubility; more than about 30 weightpercent of the esters, ethers and ketone illustrated in Group (1) hasthe same effect; and, finally, if X in Group (2) is more than about 40weight percent alcohol or ketone residues, solubility is also adverselyaffected. However, incorporation of other A groups, or acrylamide oracrylic acid or acid salt monomers for the remainder of the copolymerwill result in sufficient solubility.

It is typical in secondary oil recovery operations to utilize brine andpolymer as the flooding medium. Often these brines contain divalentions, such as Ca, which may precipitate the polymer. Therefore, thepreferred mobility control polymers are those which do not precipitatein the presence of, for instance, Ca. Preferred polymers, then, areselected from the following group:

where m p is greater than about 35, p is less than about 65, n isgreater than about 15, m n +p 100, Y 15 as above defined and Z isgreater than about 200;

1 i311 i i each R is H or -CH;,, m p is greater than about 35, n +p isgreater than about 15, m n +p 100, Y is as above defined and is greaterthan about 200;

' Ha-CH cm-cH CHa-CH 1 NH: in '*Y*' n SO8 Y+ wherein m +p is greaterthan about 35, n p is greater wherein m is greater than about 35, n isgreater than about 1 5, m n 100, Y is as defined above and Z is greaterthan about 200. Those polymers of Group 4 are the most preferred.

The polymer conserving agents which are suitable herein comprise watercontaining from about 0.005 to 50 weight percent of at least onewater-soluble polymer selected from the group defined by the aboveformula, wherein, in said formula, m, n and p may each vary from O to100, m n +p equaling Z is less than about 70, preferably from about 0.2to about 60; and ,R, R, Y and A are as defined above. Said conservingagents typically have a molecular weight between about 2,000 and about500,000. Said agents are generally prepared from the same types ofmonomers as used for the mobility control polymers, the above sourcesregarding the description and preparation of the mobility controlpolymers being also applicable to the conserving agents. The preferredpolymer conserving agents are also selected from the above groups (1-4).In addition, a preferred species is described when m and p are 0, n is100, R is H, the other variables being as above described.

The polymer conserving agent is suitably introduced into the formationto be treated in an amount equal to from about 0.1 to 100 percent of thepore volume of said formation.

Both the mobility control polymers and the polymer conserving agents aresuitable for use in either essentially pure water or in brines. The termwater is used throughout to include brines as well as pure water.

The recovery enhancing material (herein referred to as REM) can be anydisplacing fluid which acts as a miscible or miscible-like displacingprocess and which preferably contains at least about 20 percent water.

Preferably the REMs are oil-external or water-external emulsions oroil-external or water-external micellar dispersions. The term micellardispersion is meant to include micellar solutions, transparentemulsions, and microemulsions. Preferably the REM is a micellardispersion containing from at least 4 to about 20 percent by volume of apetroleum sulfonate which preferably has an average equivalent weightwithin the range of about 350 to about 525; at least about 20 and up toabout 94 percent by volume of water; about 2 to about 75 percent byvolume of hydrocarbon; and optionally about 0.1 to about 20 percent byvolume or more of a cosurfactant which preferably is an alcohol, ester,aldehyde, ketone, ether, mixture thereof, or like compound(s) containingone to about 20 or more carbon atoms and/or about 0.01 to about 5percent, weight percent based on the water, of an electrolyte whichpreferably is an inorganic acid, inorganic base, or inorganic salt.Examples of useful REMs are defined in U. S. Pat. Nos. 3,254,714 toGogarty et al.; 3,497,006 to Jones et a1; 3,506,070 and 3,506,071 toJones; 3,330,344 and 3,348,611 to Reisberg; 3,126,952 to Jones;3,373,809 to Cooke, Jr.; 3,288,213 to King et al.; 3,126,952 to Jones;3,163,214 to Csaszar; 3,512,586 to Holm; 3,302,713 to Ahearn et al.;3,149,669 to Binder, Jr., et al.; 3,208,515 to Meadors; and 3,208,517 toBinder, Jr., et al.

Where the aqueous PCA solution precedes the REM, it is preferred thevolume amount (percent pore volume) of PCA injected be about 0.1 toabout 100 percent, preferably 0.5 to about 40'percent and morepreferably about 1 to about 20 percent formation pore volume. Also, thePCA can be present in concentrations of about 0.005 to about 50 weightpercent or more, preferably 0.05 to about 5.0 percent and morepreferably about 0.1 to about 1 percent by weight. The aqueous solutioncontaining the PCA can contain other additives to impart desiredproperties to the flooding process.

Where the PCA is incorporated into the REM slug, the concentration ofthe PCA can be about 0.01 to about 5 percent or more and preferablyabout 0.025 to about 2.5 percent and more preferably about 0.05 to about1 percent by weight, based on the aqueous medium within the REM. Asmentioned earlier, it is preferred that the REM contain at least 20percent water. Preferably the REM is a micellar dispersion and morepreferably a water-external micellar dispersion containing about 40 toabout 95 percent by volume water.

After the REM slug is injected, an aqueous slug containing the mobilitycontrol polymer is injected (formation pore volumes of the mobilitycontrol polymer of about 5 to about 75 percent or more and preferablyabout to about 50 percent are useful). Thereafter, a water drive isinjected to displace the previously injected slugs toward the productionmeans in fluid communication with the subterranean reservoir to recovercrude oil therethrough.

In the preceding discussion, it has been assumed that the PCA is to beemployed in quantities such that adsorption of the mobility controlpolymer will be prevented throughout the swept portion of the reservoir.This is necessary if a denuded bank of water is absolutely to beavoided. However, there are circumstances where some adsorption of thepolymer may be allowed without loss of recovered oil. For example, itmight be true that adsorption might be allowed to occur during the lastquarter of the displacement process. The resulting bank of water wouldbe insufficient in volume to finger throughout the REM slug before theflood is complete. When a situation like this exists, the quantity ofPCA may be decreased by about 25 percent.

It should be made clear that the discussion above involves two distinctsituations. Firstly, the REM slug is of such a nature that it can beformulated to match the mobility of the mixed oil-water bank which itdisplaces. This is true of the micro-emulsion system proposed byGogarty. Some other REMs, such as alcohols and the like, might requirethe incorporation of special materials for mobility reduction. In thesecases, adsorption of the mobility control polymer results in theproduction ofa high mobility water bank between the polymer and the REM.This results in penetration and destruction of the REM. Secondly, theREM may be a water-based material, such as a surfactant solution.Employed without modification, it may be very inefficient in displacingthe oil-water mixture which it is forming by the displacement of thereservoir fluids. This may be due to relative permeability effects or toviscous fingering. But, it occurs because the mobility of the REM isgreater than the mobility of the oil-water mixture it is displacing.This inefficiency is reduced or eliminated by using the mobility controlpolymer, not only behind the REM, but in the REM as well. In this case,adsorption results in the formation of a deleterious high mobility REMbank between the low mobility REM bank and the mixture of oil and waterwhich preceeds it through the reservoir. The PCA prevents the fingeringof this polymer stripped portion of the REM slug through the oil-waterbank which it is attempting to drive ahead of it.

SPECIFIC EMBODIMENTS 1. Oil in a particular field is produced by primarymeans, and then by water-flooding to near the economic limit. At the endof water-flooding, a large amount of the original oil in place remainsin the pore spaces of the rock as an irreducible oil saturation. (Thisresidual oil saturation is recognized as being due to entrapment byinterfacial forces.) Reservoir parameters and the water-flood behaviorindicate that this reservoir is a candidate for tertiary recovery usingan oil external micellar solution as proposed by Gogarty (US. Pat. No.3,406,754). A small volume (about five percent of the reservoir porevolume) of the micellar solution will be used. The micellar fluid willdisplace the residual oil from the pore spaces and drive it, and thewater left from water-flooding, through the reservoir. The oil and waterwill precede the REM through the reservoir as a mixed bank. By themethods indicated by Gogarty, the mobility of the REM will be adjusteduntil it is equal to or less than the mobility of the mixed oil andwater bank which precedes it. This will prevent bypassing of theoil-water bank by the REM bank because of miscible fingering.

As Gogarty indicates, it is necessary to reduce the mobility of thewater following the REM to prevent deleterious fingering of the waterthrough the reduced mobility REM. (These factors are thoroughlyconsidered in GOGARTY, MEABOM, & MILTON, Mobility Control Design forMiscible-Type Water-floods Using Micellar Solutions. .1. Pet. Tech., p.141, Feb. (1970). This is to be accomplished through the use of ahydrolyled pqly m m i itx ssiusin ,PQ ms Laboratory tests in specimensof the formation from the subject field indicate that the desiredreduction in mobility can be achieved through the use of 500 ppm of thepolymer. However, laboratory tests also indicate that the polymer willbe adsorbed to the extent of 300 pounds of polymer for each acre-foot offormation exposed to the polymer solution. If this adsorption occurs, alarge volume of high mobility, polymer-free water will be producedbetween the front of the polymer solution and the back of the micellarrecovery enhancing agent. If this is allowed to occur, the water willpenetrate the small slug of the micellar fluid, which will be bypassedto an undesirable degree. Heterogeneity in the reservoir will accentuatethe bypassing. This effect can be eliminated by injecting into theformation a polymer conserving agent ahead of the micellar solutionslug. A good example would be a relatively low molecular weighthydrolyzed polyacrylamide.

Laboratory tests are run to determine the adsorption loss of the PCA onthe formation. The methods of the aforementioned application may beused. The total amount of PCA to be injected is calculated from thereservoir volume to be treated and the value of the adsorption lossdetermined in said laboratory tests.

It is desirable that the PCA solution used ahead of the REM not have amobility in the reservoir greatly lower than that of water. This isbecause the PCA will be present in the aqueous phase of the mixedoil-water bank which is driven by the REM, and the mobility of the mixedbank can be reduced if the mobility of the PCA is much lower than thatof water. (The importance of this effect can be calculated from themethods given in the above paper by Gogarty). Significant reduction inthe mobility of the mixed bank would require further adjustment in theREM and an increase in the level of mobility control polymer followingthe REM. To prevent a significant mobility increase, the molecularweight of the PCA selected is as low as possible, and the PCA is used ata concentration which does not produce a significant increase in theviscosity of the water. It is preferable to use water of a salinityequal to 0.5 percent sodium chloride or greater for the PCA solution.This will have the effect of keeping the viscosity down. This would beundesirable if laboratory measurements indicated that the added saltincreased PCA adsorption significantly.

Consistent with these considerations of mobility, the PCA solution wouldnormally be injected at as high a concentration as possible until therequired weight of agent had been started through the reservoir. If, forexample, the PCA adsorption is found to be 300 lbs. per acre-foot offormation, and a practical volume for injection into the reservoir ispercent of the pore volume of a reservoir rock of percent porosity, thenthe PCA concentration can be calculated to be approximately 0.9 percent.

To assure that the system is workable, a test core is saturated withwater and oil to simulate the conditions :which would exist at the endof water-flooding. This As a result of the preceding test program, thefollowing materials are sequentially injected into the reservoir:

1. A 5 percent slug of a 0.9 percent solution of the PCA.

2. A 5 percent slug of the micellar solution.

3. Mobility control polymer solution of kind, concentration, and volumeindicated by methods similar to those described by Gogarty.

11. Core tests were run to determine the effect on oil production ofutilizing a PCA in advance of a REM.

Berea sandstone cores 4 feet long X 3 inches in diameter were preparedfor tertiary flooding by first saturating the cores with watercontaining 18,000 ppm of TDS (total dissolved solids), thereafterflooding the cores with crude oil having a viscosity of 7 cp at 22C. toresidual water saturation and then flooding the cores with the 18,000TDS water to residual oil saturation. The cores had permeabilities ofabout 100-200 md (millidarcies).

The cores were then flooded in the indicated sequence with watersolutions of a PCA, a micellar solution and a mobility control polymer.The water referred to contained about 500 ppm of TDS.

The PCA utilized is defined by the above generic for- ,mula when m and nare 50, p is 0, Y is Na, R and R and H and Z is about 2,500. Themobility control polymer utilized was Dow PUSHER 700, available from TheDow Chemical Company, Midland, Michigan. The micellar solution contained14.5 percent of an ammonium petroleum sulfonate (average equivalentweight 410), 4.2 percent vehicle oil (from the sulfonate), 8.3 percentcrude oil having a viscosity of 7 cp at 22C., 59.5 percent distilledwater, 2.8 percent of inorganic salt, and 0.6 percent of primaryhexanol, the percents based on weight. In all the cases, watercontaining 500 TDS was injected to displace the slugs through the cores.

The sequence and results are given below:

Oil Run Description of Flood Recovered 1 4% PV (pore volume) of themicellar solution is followed by PV of water containing 300 ppm of DowPUSHER 700 polymer.

2 4% PV of the micellar solution followed by 10% PV of water containing5,000 ppm of PCA and 300 ppm Dow PUSHER 700 polymer and then 60% PV ofwater containing 300 ppm of Dow PUSHER 700 polymer 3 10% PV of watercontaining 5,000 ppm of PCA, then 4% PV of the micellar solutionfollowed by 70% PV of water containing 300 ppm of Dow PUSHER 700polymer.

4 47V of the micellar solution followed by PV of water containing 600ppm of Dow PUSHER 700 polymer.

5 4% PV of the micellar solution followed by 10% PV of water containing5,000 ppm of PCA and 600 ppm of Dow PUSHER 700 polymer and then 60% PVof water containing 600 ppm of Dow PUSHER 700 polymer.

6 10% PV of water containing 5,000 ppm of PCA followed by 4% PV of themicellar solution and then 70% PV of water containing 600 ppm of DowPUSHER 700 polymer.

The above data clearly indicates the polymer conserving agent improvesoil recoveries and especially so area madman @515};airaragEmigration arecovery enhancing material comprising a miscible'or miscible-likedisplacing fluid and a flooding medium comprising water containing from0.001 to 0.5 weight percent of a water-soluble organic mobility controlpolymer having a molecular weight of at least about 1.5 X said polymerbeing of the formula hai l .3214 \l ll izfl. i....l. l.

wherein each R is H or CH; and X is wherein X, is O--Y NH or OR .(R'being CH or CH,CH or Rt wherein R and R are, independently, H or -CH theim rdveaehr 'com' riahg 711563655; raakad input well or wells prior toor concurrently with the recovery enhancing material an amount of apolymer conserving agent which equals from about 0.1 to 100 percent ofthe pore volume of the formation to be treated, said polymer conservingage ht comprising water containing from about 0.005 to 50 weight percentof at least one water-soluble polymer selected from the group defined bythe above formula, wherein, in said formula, Z is less than about 70,the other variables being as defined above.

2. The process of claim 1 wherein, in the formula describing themobility control polymer, n varies from 0 to about 67 and p varies from0 to about 33.

3. The process of claim 1 wherein, in the formula describing the polymerconserving agents, Z varies from about 0.2 to about 60.

4. The process of claim 1 wherein the flooding medium comprises watercontaining from about 0.01 to 0.15 weight percent of the mobilitycontrol polymer.

5. The process of claim 1 wherein the molecular weight of the mobilitycontrol polymer is at least about 2.5 X 10 6. The process of claim 1wherein the polymer conserving agent comprises water containing fromabout 0.05 to 5 weight percent of polymer.

7. The process of claim 1 wherein the polymer conl serving agent isemployed at from about 0.5 to 40 percent of the pore volume.

8. The process of claim 1 wherein the mobility control polymer isselected from the group:

Y is H*, -NH or an alkali or alkaline earth metal ion; and Z is greaterthan about 200;

GEL iNLJ awhenmnlmailljs ii? iii). A

wherein X is each R is l-l or --Cl-I m p is greater than about 35, n +pis greater than about 15, m n +p= and Y and Z are as above;

CHz-CH CHaCH CHa-OH i izflmi h).

wherein m +p is greater than about 35, n -l-p is greater than about 15,m n +p =100 and Y and Z are as above; or

CH CH ll izflml cn, -cacmou Lk (:0) K =o I IHQ m 4)-Y+ n Z wii'riii m isgfeater than about 35, n is greater thaif about 15, m +p 100 and Y and Zare as above, and

the polymer conserving agent is water containing a' polymer of theformula CHz-CH ii 512M vvherein Z is between about 0.2 and 60, and Y, mand n are as above defined.

11. The process of claim 1 wherein, in the formula describing thepolymer conserving agents, m and p are 0, n is 100 and R is H, the othervariables being as defined therein.

12. The process of claim 1 wherein the recovery enhancing materialcontains at least about 20 percent by volume of water.

13. The process of claim 1 wherein the recovery enhancing material is anoil-external emulsion, a waterexternal emulsion, an oil-externalmicellar dispersion or a water-external micellar dispersion.

14. The process of claim 1 wherein the recovery enhancing material is amicellar dispersion containing from about 20 to about 94 volume percentof water.

15. The process of claim 1 wherein the recovery enhancing material is amicellar dispersion containing from at least 4 percent to about 20percent by volume of a petroleum sulfonate; at least about 20 percentand up to about 94 percent by volume of water; about 2 percent to about75 percent by volume of hydrocarbon; and, optionally, about 0.1 to about20 percent by volume Or more Of a cosurfactant.

V 7 104050 UNITED STATES PATENT OFFICE R IFIQAT er (IQRRECTION PatentNo. 3,7833% 7 I Dated January .8, 1971;

. fi m-( R. Jennings and W. M. Thornton .I [t is certified that .errcrappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Column 2, lines 18 end 19 a. phrase has "been left put. The entire twolines with the proper additions should read:

---- line ealfh (such ae Mg or Ca f) metal ion; in is 0 to 100;

n is 0 to 100, preferably 0 to about 6 7,; p is o to 100, preferably Obo about 33; m n 1) equal 100; Z

Colrmn 2,, mes 22 thrdugh 26 should be:

+ s CH c .whereirl i r -CH a.n d is Column 2, line. he should be:

wherein each R is 1i or -cH @52 is Column 2 Iaet line should. be:

-- wherein R and' R'L are, independently, H or CH Certificate bfCorrectiori U.S. Patent N .-..3.,783,9M

7 Column &5 line l0 should. be: I

Column 10, line 28 should. be:

Signed and seeled this 19th day of November. 1974.

(SEAL) Atte st Page 2 Dated January '8, 197

c. MARSHALL DANN Comissipner of Patents

2. The process of claim 1 wherein, in the formula describing themobility control polymer, n varies from 0 to about 67 and p varies from0 to about
 33. 3. The process of claim 1 wherein, in the formuladescribing the polymer conserving agents, Z varies from about 0.2 toabout
 60. 4. The process of claim 1 wherein the flooding mediumcomprises water containing from about 0.01 to 0.15 weight percent of themobility control polymer.
 5. The process of claim 1 wherein themolecular weight of the mobility control polymer is at least about 2.5 X106.
 6. The process of claim 1 wherein the polymer conserving agentcomprises water containing from about 0.05 to 5 weight percent ofpolymer.
 7. The process of claim 1 wherein the polymer conserving agentis employed at from about 0.5 to 40 percent of the pore volume.
 8. Theprocess of claim 1 wherein the mobility control polymer is selected fromthe group:
 9. The process of claim 8 wherein the polymer conservingagent is water containing at least one polymer selected from the group Ato D in said claim 8, wherein, in the formulas, Z is greater than about0.2 but less than about 60, the other variables being as definedtherein.
 10. The process of claim 1 wherein the mobility control polymeris of the formula
 11. The process of claim 1 wherein, in the formuladescribing the polymer conserving agents, m and p are 0, n is 100 andR'' is H, the other variables being as defined therein.
 12. The processof claim 1 wherein the recovery enhancing material contains at leastabout 20 percent by volume of water.
 13. The process of claim 1 whereinthe recovery enhancing material is an oil-external emulsion, awater-external emulsion, an oil-external micellar dispersion or awater-external micellar dispersion.
 14. The process of claim 1 whereinthe recovery enhancing material is a micellar dispersion containing fromabout 20 to about 94 volume percent of water.
 15. The process of claim 1wherein the recovery enhancing material is a micellar dispersioncontaining from at least 4 percent to about 20 percent by volume of apetroleum sulfonate; at least about 20 percent and up to about 94percent by volume of water; about 2 percent to about 75 percent byvolume of hydrocarbon; and, optionally, about 0.1 to about 20 percent byvolume or more of a cosurfactant.